PINs are part of the RIM infrastructure. A message can be sent from one PIN to another. BB Messenger also uses PINs. For corporations, only the latest BES 4.1 allows auditing of PIN messages. Prior to that people used it for privacy and to get into ATMS

PIN messages are included in your data plan. That means no extra SMS package for you buddy! The only downfall, I know very few people with a Blackberry that I feel the need to pin, so i need an SMS package